The oxygen reduction reaction (ORR) is an important electrode reaction for energy storage and conversion devices based on oxygen electrocatalysis. This paper introduces the thermodynamics, reaction kinetics, reaction mechanisms, and reaction pathways of ORR in aqueous alkaline media. Recent advances of the catalysts for ORR were extensively reviewed, including precious metals, nonmetal-doped carbon, carbon–transition metal hybrids, transition metal oxides with spinel and perovskite structures, and so forth. The applications of those ORR catalysts to zinc–air batteries and alkaline fuel cells were briefly introduced. A concluding remark summarizes the current status of the reaction pathways, advanced catalysts, and the future challenges of the research and development of ORR.

Well-separated RGO sheets decorated with MnO2 nanoparticles facilitate easy access of the electrolyte ions to the high surface area of the paper electrode, enabling the fabrication of a thicker electrode with heavier areal mass and higher areal capacitance (up to 897 mF cm(-2) ). The electrochemical performance of the bent asymmetric device with a total active mass of 15 mg remains similar to the one in the flat configuration, demonstrating good mechanical robustness of the device.

In this paper, a very simple solution-based method is employed to coat amorphous MnO2 onto crystalline SnO2 nanowires grown on stainless steel substrate, which utilizes the better electronic conductivity of SnO2 nanowires as the supporting backbone to deposit MnO2 for supercapacitor electrodes. Cyclic voltammetry (CV) and galvanostatic charge/discharge methods have been carried out to study the capacitive properties of the SnO2/MnO2 composites. A specific capacitance (based on MnO2) as high as 637 F g(-1) is obtained at a scan rate of 2 mV s(-1) (800 F g(-1) at a current density of 1 A g(-1)) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 50 A g(-1) are 35.4 W h kg(-1) and 25 kW kg(-1), respectively, demonstrating the good rate capability. In addition, the SnO2/MnO2 composite electrode shows excellent long-term cyclic stability (less than 1.2% decrease of the specific capacitance is observed after 2000 CV cycles). The temperature-dependent capacitive behavior is also discussed. Such high-performance capacitive behavior indicates that the SnO2/MnO2 composite is a very promising electrode material for fabricating supercapacitors.

Highly active and durable air cathodes to catalyze both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for rechargeable metal-air batteries. In this work, an efficient bifunctional oxygen catalyst comprising hollow Co O nanospheres embedded in nitrogen-doped carbon nanowall arrays on flexible carbon cloth (NC-Co O /CC) is reported. The hierarchical structure is facilely derived from a metal-organic framework precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC-Co O /CC can be used as an additive-free air cathode for flexible all-solid-state zinc-air batteries, which present high open circuit potential (1.44 V), high capacity (387.2 mAh g , based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt- and Ir-based zinc-air batteries.